In traditional Hybrid Fiber-Coax (HFC) systems for Cable Television systems, Fiber Nodes (FN) are intermediate sub-systems in an overall information distribution network hierarchy. From least to highest bandwidth concentration, the network hierarchy includes subscribers (generally homes), FNs, secondary hubs (SHs), primary hubs, and the headend.
FNs interface with the SHs optically and interface with the subscribers over active RF coaxial networks (i.e., networks of coaxial cable interspersed with active RF distribution amplifiers as required for signal integrity). FNs may serve between 600 and 1200 subscribers. This can be accomplished by segmenting the total number of subscribers into “buses” of 300 subscribers. A cascade of five to eight RF amplifiers may exist between the FN and any given subscriber. Four to six fibers may couple the FN to a SH.
FIGS. 1A through 1C illustrate a prior-art HFC cable system having return channels wherein the primary processing is performed at the cable Head End. These return channels can include DOCSIS signals from cable modems and so-called legacy signals, which include conventional analog telephone signals and RF modulated digital signals with proprietary encoding schemes that remain encoded until receipt at the head end. FIG. 1A is a top-level view of the cable system, including the cable system head-end and the customer premises equipment (CPE). FIG. 1B provides additional detail of the CPE of FIG. 1A. FIG. 1C provides additional detail of the NID of FIG. 1B.
Recent variants to the above HFC architecture have been based on so-called mini fiber nodes (mFNs), a FN variant that is both smaller and deeper into the network (closer to the subscriber) than a traditional FN. FIG. 2A illustrates an HFCN incorporating such mFNs in conjunction with FNs. The in FNs are generally distinguished from FNs in that they interface with only 50 to 100 subscribers and the path from mFN to subscriber is via an all passive coaxial network. The mFN distributes downstream information to the subscribers and aggregates upstream information from subscribers. The mFN interfaces via optical fiber to the next higher level in the hierarchy.
There are many possible topologies for mFN-based HFC systems and the exact functionality of an mFN will vary with the system topology. In a first example, MFNs can be used as part of a fiber overlay to upgrade traditional “trunk-and-branch” coaxial systems, or HFC systems with downstream only FNs, with return path (upstream) services (e.g., for Cable Modems). In such applications, the optical return (upstream) path is routed from the mFN directly to the SH, bypassing the downstream only path (which in an HFC system includes FNs). This in effect configures each line extender with a return fiber that provides each passive span with a unique return spectrum. FIGS. 2A and 2B illustrate such a prior-art HFC cable system having a packet fiber overlay using mini-FiberNodes (mFNs). FIG. 2A is a top-level view of the HFC/mFN cable system. FIG. 2B provides additional detail of the mFNs of FIG. 2A. In a second example, mFNs can be used with “MuxNodes” that replace a single FN or consolidate multiple FNs. MuxNodes not only “distribute” (demultiplex) information downstream but also “aggregate” (multiplex) information upstream (from subscriber to provider).
In either architecture—using FNs or mFNs, or a combination of the two—the bandwidth of the upstream path from an FN or mFN has previously been inefficiently utilized. The FN or mFN has heretofore re-transmitted the entire 5-42 MHz return spectrum to upstream hubs, though in most cases only a small portion of that spectrum is actually desired or will be utilized. The entire spectrum has been transmitted upstream because the bulk, cost and power consumption of the equipment required to process the upstream signal and pass on only the desired components has prohibited its deployment in the field.
In previous systems every upstream channel has required a respective splitter tap, receiver input including a bulkhead-mount connector, and cabling between the splitter tap and the receiver input. Such components, especially the high number of connectors, add cost and bulk that would otherwise not be expended, as well as introducing new noise. Additionally, previous systems have required manual adjustments or manual changing of plug-in components, in order to provision or reprovision a channel.
The aforementioned manual configurations of cabling and channel adjustments have been necessary at initial installation and often many times thereafter. Node recombining (e.g., manual recabling to pair a new logical channel with a new line card) has often been necessary whenever an existing subscriber channel reaches capacity and additional channels need to be assigned. Manual channel reprovisioning has also been frequently necessary to avoid various sources of ingress noise, which varies both in time and channels affected.
What is needed is an ability to efficiently process upstream signals in a cost- and space-effective way that can be done close to the subscriber, that reduces hardware introduced noise and minimizes the need for manual intervention when reprovisioning a channel.
A general discussion of HFC architectures, with a particular focus on mFN-based systems, is provided by the article “HFC architecture in the making: Future-proofing the network,” by Oleh Sniezko, et al, in the July 1999 issue of Communications Engineering & Design Magazine (CED Magazine), published by Cahners Business Information, a member of the Reed Elsevier plc group.
“DOCSIS” is a family of interoperability certification standards for cable modems. “OpenCable” is a family of interoperability specifications directly and indirectly related to digital set-top box hardware and software interfaces. “PacketCable” is a family of specifications aimed at facilitating real-time, multimedia packet-based services, using a DOCSIS-managed regional access network as the foundation. While having broad applicability, an initial focus of PacketCable is VoIP (Voice over Internet Protocol). Cable Television Laboratories, Inc. (CableLabs), with offices in Louisville, Colo., is a research and development consortium of North and South American cable television operators. CableLabs manages, publishes, and distributes a number of specifications and certification standards related to various aspects of Cable Television systems, including the DOCSIS, OpenCable, and PacketCable standards families.
The International Telecommunications Union (ITU), headquartered in Geneva, Switzerland, is “an international organization within which governments and the private sector coordinate global telecom networks and services.” The ITU manages, publishes, and distributes a number of international telecom related standards. Standards relevant to Cable Television systems include the ITU-T Series H Recommendations and the ITU-T Series J Recommendations. The “-T” stands for Telecommunications. Series H covers all ITU-T standards for “audiovisual and multimedia systems.” Series J covers all ITU-T standards for “transmission of television, sound programme and other multimedia signals.”